I recently picked up a '29 AA t5ruck that has been sitting since 1951. After breaking the engine loose, freeing up a couple stuck valves I finally got the dependable old Model A started. It has been rebuilt (I guess) sometime in the past since it has adjustable valves. It has an old pressure gauge and when warm it still shows 15# oil. I didn't think these engine would produce that kind of pressure> Why?